APs and multiple BSSID support (OT?)

Bob Carlson rjc at sigpro.com
Wed Feb 7 01:05:50 EST 2007


> -----Original Message-----
> From: hostap-bounces+bob.carlson=sigpro.com at shmoo.com [mailto:hostap-
> bounces+bob.carlson=sigpro.com at shmoo.com] On Behalf Of Jouni Malinen
> Sent: Tuesday, February 06, 2007 9:01 PM
> To: hostap at shmoo.com
> Subject: Re: APs and multiple BSSID support (OT?)
> 
> On Tue, Feb 06, 2007 at 10:06:41AM -0700, Bob Carlson wrote:
> > Perhaps this is a little OT, but this seems like a good community to
> which
> > to address this question. I'm using wpa_s in a Wifi client device that
> acts
> > like multiple virtual clients. One key problem is APs that support
> multiple
> > SSIDs. Atheros calls these virtual APs. Cisco doesn't call them
> anything,
> > they just refer to "multiple SSIDs". Unlike the Atheros code that I am
> > familiar with, Cisco allows multiple SSIDs on a single BSSID, but you
> can
> > enable multiple BSSIDs.
> 
> Could you please describe the problem in bit more detail than it just
> existing.. Rest of your email seems to be about the AP side, but if I
> understood correctly, the problem you are describing is for the virtual
> client device.

I am trying to make hardware designed to be either an AP with virtual APs
or a single client into a client that can act as if it is two virtual
clients. The client type functions in the hardware are not fully suited to
this. For example, the source address is used to select the key for
hardware decryption, so I do software decryption.

The problem with mult. SSID/BSSIDs is that there is no way to make the
hardware aware of 2 different BSSIDs for things like timing derived from
the beacons. I believe I can connect to two different BSSIDs if they are
supported by the same physical AP. Beacons from the same physical AP will
share many attributes such as timing, channel, rates, etc.

That's a long winded explanation for a simple need. Because I can only
successfully connect to 2 different BSSIDs if they are supported by the
same physical AP, I would like a way to determine that. The Atheros and
Cisco address methods allow me to do that. However, if other vendors choose
their multiple BSSIDs differently (I have seen a proposal that the BSSID be
generated randomly in the local space) I don't see any way to determine
"same physical AP."

If there is another way to determine whether 2 beacons or probe responses
with different BSSIDs come from the same physical AP, I would love to hear
of it.
 
> > In the Atheros case, when more than one BSSID is needed, they generate
> it
> > using the private mac address space.
> 
> > Cisco uses a more straightforward approach, just adding 1 to byte 5.
> 
> > Does anyone know of any other different methods of generating multiple
> > BSSID?
> 
> Yes.. Depending on the hw design, one could use any of the BSSID bits
> (apart from local and broadcast) to generate new addresses. Local
> address space makes it easier to get large number of addresses, but if
> one happens to have a large space of addresses available, it would be
> possible to allocate set of addresses for each device (though, IEEE
> might get somewhat unwilling to allocate more OUIs for this kind of
> address use if large portion of the addresses are not really used).
> 
> Different designs might support list of arbitrary addresses or some sort
> of bitmask on the addresses, so at least in theory, the sets of
> addresses could be quite diverse.

Yes, I know that theoretically the addresses could be anything including
random. I was hoping to find information on what specific vendors do.

> --
> Jouni Malinen                                            PGP id EFC895FA


Thanks, Bob




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